CVE-2026-25885
📋 TL;DR
CVE-2026-25885 is an authentication bypass vulnerability in PolarLearn's WebSocket group chat functionality. Unauthenticated attackers can subscribe to any group chat and send messages that are permanently stored, affecting all users of PolarLearn 0-PRERELEASE-16 and earlier.
💻 Affected Systems
- PolarLearn
📦 What is this software?
Polarlearn by Polarlearn
⚠️ Risk & Real-World Impact
Worst Case
Attackers could inject malicious content, impersonate legitimate users, disrupt educational activities, and potentially use chat messages as a vector for further attacks like XSS or phishing.
Likely Case
Unauthenticated users spamming group chats with inappropriate content, disrupting learning environments, and compromising chat integrity.
If Mitigated
With proper authentication controls, only authorized users can access group chats, maintaining chat integrity and preventing unauthorized message injection.
🎯 Exploit Status
Exploitation requires only WebSocket client tools and knowledge of group UUIDs, which could be discovered through enumeration.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after commit 3ba588fda0d3f8e238483a20772719f27e52e79f
Vendor Advisory: https://github.com/polarnl/PolarLearn/security/advisories/GHSA-gvjm-5pw7-6c8c
Restart Required: Yes
Instructions:
1. Update PolarLearn to a version containing commit 3ba588fda0d3f8e238483a20772719f27e52e79f or later. 2. Restart the PolarLearn service. 3. Verify authentication is now required for WebSocket connections.
🔧 Temporary Workarounds
WebSocket Authentication Enforcement
allImplement authentication checks before allowing WebSocket connections to group chats
Not applicable - requires code changes
Network Access Control
linuxRestrict access to the WebSocket endpoint (wss://polarlearn.nl/api/v1/ws) to authenticated users only via reverse proxy or firewall rules
# Example nginx location block to require auth
location /api/v1/ws {
auth_request /auth;
proxy_pass http://backend;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
}
🧯 If You Can't Patch
- Implement network-level authentication proxy in front of the WebSocket endpoint
- Disable group chat functionality entirely if not essential
🔍 How to Verify
Check if Vulnerable:
Attempt to connect to wss://your-instance/api/v1/ws without authentication and send a message to any known group UUID. If successful, the system is vulnerable.Check Version:
Check PolarLearn version in admin interface or configuration filesVerify Fix Applied:
Attempt the same connection without authentication - it should be rejected or require valid credentials.📡 Detection & Monitoring
Log Indicators:
- WebSocket connections without authentication tokens
- Chat messages from unauthenticated users
- Failed authentication attempts followed by successful WebSocket connections
Network Indicators:
- WebSocket traffic to /api/v1/ws without authentication headers
- Unusual chat message patterns from unknown sources
SIEM Query:
websocket AND (uri_path:"/api/v1/ws") AND NOT (authentication_token:*)